// char get() const { return contents[cursor]; }//using Action_c_v = char
// (Screen::*)()const; char get_cursor() const { return contents[cursor];
// }//同上 inline char get(pos ht, pos wd) const;//using Action_c_uu = char
// (Screen::*)(pos,pos)const; Screen &move(pos r, pos c);//using
// Action_Screen_uu = Screen &(Screen::*)(pos,pos);